U.S. patent application number 10/632813 was filed with the patent office on 2005-02-10 for method of controlling reverse link transmission.
Invention is credited to Vasudevan, Subramanian, Yang, Yunsong.
Application Number | 20050030953 10/632813 |
Document ID | / |
Family ID | 34115796 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050030953 |
Kind Code |
A1 |
Vasudevan, Subramanian ; et
al. |
February 10, 2005 |
Method of controlling reverse link transmission
Abstract
The method of controlling reverse link transmission by at least
one mobile station includes first scheduling a transmission by at
least one mobile station by sending a schedule grant message
according to a first scheduling protocol. The schedule grant
message provides the mobile station with approval to transmit, and
further establishes a rate limit for transmissions scheduled
according to a second scheduling protocol.
Inventors: |
Vasudevan, Subramanian;
(Morristown, NJ) ; Yang, Yunsong; (Piscataway,
NJ) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. Box 8910
Reston
VA
20195
US
|
Family ID: |
34115796 |
Appl. No.: |
10/632813 |
Filed: |
August 4, 2003 |
Current U.S.
Class: |
370/395.4 ;
370/342 |
Current CPC
Class: |
H04W 52/325 20130101;
H04W 72/1289 20130101; H04L 47/14 20130101; H04L 47/263 20130101;
H04W 28/0289 20130101; H04W 28/22 20130101; H04L 47/10
20130101 |
Class at
Publication: |
370/395.4 ;
370/342 |
International
Class: |
H04L 012/56 |
Claims
We claim:
1. A method of controlling reverse link transmission by at least
one mobile station, comprising: first scheduling a reverse link
transmission by at least one mobile station by sending a schedule
grant message according to a first scheduling protocol, the
schedule grant message providing the at least one mobile station
with approval to transmit, the schedule grant message further
establishing a rate limit for transmissions scheduled according to
a second scheduling protocol.
2. The method of claim 1, wherein the first scheduling protocol is
a scheduling mode protocol and the second scheduling protocol is a
rate control mode protocol.
3. The method of claim 1, further comprising: second scheduling a
subsequent reverse link transmission by the mobile station by
sending a rate control instruction according to the second
scheduling protocol.
4. The method of claim 3, wherein the first scheduling step sends
the schedule grant message over a first forward control channel and
the second scheduling step sends the rate control instruction over
a second forward control channel.
5. The method of claim 3, wherein the rate control instruction
indicates to transmit at the rate limit.
6. The method of claim 5, wherein a failure to send a rate control
instruction indicates not to transmit.
7. The method of claim 3, wherein the rate control instruction
indicates one of an increase and a decrease in the rate limit.
8. The method of claim 3, further comprising: sending another
schedule grant message that resets the rate limit.
9. The method of claim 3, further comprising: determining a change
in rate limit between a previously scheduled transmission and a
currently scheduled transmission; and performing the second
scheduling step when the determined change does not exceed a
threshold amount.
10. The method of claim 1, further comprising: sending another
schedule grant message that resets the rate limit.
11. A method of controlling reverse link transmission by at least
one mobile station, comprising: scheduling a reverse link
transmission by at least one mobile station by sending a schedule
grant message according to a first scheduling protocol, the
schedule grant message providing the at least one mobile station
with approval to transmit, the schedule grant message resetting a
rate limit for transmissions scheduled according to a second
scheduling protocol.
12. The method of claim 11, wherein the first scheduling protocol
is a scheduling mode protocol and the second scheduling protocol is
a rate control mode protocol.
13. A method of making reverse link transmission, comprising:
transmitting based on a rate limit set by a previously received
schedule grant message if a rate control instruction is
received.
14. The method of claim 13, wherein the previously received
schedule grant message is received over a first channel and the
rate control instruction is received over a second channel.
15. The method of claim 13, further comprising: reducing the rate
limit if no rate control instruction is received; and increasing
the rate limit if a rate control instruction is received.
16. The method of claim 13, further comprising: adjusting the rate
limit based on an accumulation of rate control instructions
received since the previously received schedule grant message.
17. A method of making reverse link transmission, comprising:
transmitting based on a rate of a previous transmission made in
response to a previously received schedule grant message if a rate
control instruction is received.
18. A method of controlling reverse link transmission by at least
one mobile station, comprising: overriding a common rate control
instruction for the at least one mobile station by sending a
schedule grant message for the at least one mobile station.
19. The method of claim 18, further comprising: first determining
whether to override a common rate control instruction for a mobile
station based on an available load at a base station; and
performing the overriding step for a mobile station when the
determining step determines to override the common rate control
instruction for the mobile station.
20. The method of claim 19, wherein the determining step determines
whether to override the common rate control instruction for the
mobile station based on the available load at the base station, an
estimated increase in the available load if the mobile station
ignores the common rate control instruction and an estimated
reduction in the available load if the mobile station transmits in
response to a schedule grant message.
21. The method of claim 19, further comprising: second determining,
for each mobile station in a set of mobile stations to be
scheduled, whether to consider the mobile station for overriding
the common rate control instruction based on a rate supported by
the mobile station and a rate limit set forth according to a
previous common rate control instruction; and performing the first
determining step with respect to the mobile stations determined in
the second determining step.
22. A method of controlling reverse link transmission by at least
one mobile station, comprising: first transmitting, at a mobile
station, according to a schedule grant message instead of a common
rate control instruction.
23. The method of claim 22, wherein the transmitting step is a
retransmission of a negative-acknowledged transmission sent in
response to a schedule grant message.
24. The method of claim 22, further comprising: second
transmitting, subsequent to the first transmitting, according a
common rate control instruction and a rate of transmission in
response to a previous common rate control instruction.
25. The method of claim 22, further comprising: setting a secondary
pilot level based on a weighted average of the secondary pilot
levels corresponding to possible transmission rates.
26. A method, comprising: transmitting a pilot signal on the
reverse link at a power derived from a rate assigned to the mobile
station for a scheduled transmission.
Description
BACKGROUND OF THE INVENTION
[0001] Development of the releases of the CDMA2000 family of
standards, as well as UMTS and other 3.sup.rd generation wireless
standards, has focused in part on enhancing the reverse link
(mobile station to base station) operation to support high-speed
packet data applications. For example, as part of the development
of 1xEV-DV Release D, a number of framework proposals to enhance
the performance of the reverse link are under consideration. These
proposals envision using two types of modes or methods for
scheduling transmissions by the mobile station: a scheduled
transmission mode and a rate control scheduling mode.
[0002] The first type, referred to as a scheduled transmission
mode, schedules transmissions by having the base station send a
schedule grant message with an explicit instruction for the mobile
station to transmit. A grant for a scheduled transmission
designates the mobile station that is to transmit as well as the
transmission format (data rate, frame/packet duration, and
transmission power) the mobile station is to employ. The rate of a
transmission is the number of information bits that constitute the
transmission divided by the time interval over which the bits are
sent.
[0003] The rate control scheduling mode on the other hand provides
a looser form of control on mobile station transmissions. Here, the
base station sends a rate control directive or instruction, which
is typically a one bit transmission, that can be either broadcast
to all mobiles in the cell/sector (common rate control) or
transmitted individually to mobile stations (dedicated rate
control). The rate control bit has a predefined meaning. For
example, according to one proposal the rate control bit indicates
whether the mobile station is to transmit at a predetermined rate
limit or not transmit at all. The non-zero rate limit is signaled
via an actual transmission to the mobile while the zero rate limit
is signaled by the base station transmitter's silence. Such a rate
control mechanism is termed on-off keying. According to another
proposal, the rate control bit indicates whether the mobile station
is to transmit at an increased or decreased rate limit. As a
further example, such as when the rate control method is being used
to affect multiple mobile stations, the rate control bit(s)
probabilistically influences the rate limit.
[0004] As will be appreciated from the above discussion, the
proposals to date envision mutually exclusively using the rate
control scheduling mode or the scheduling transmission mode. For
example, according to one proposal, the scheduling transmission
mode is used with mobile stations that are not involved in a soft
hand-off (a mobile is said to be in soft handoff if it is in
simultaneous communication with at least two base stations that are
not collocated), and the rate control scheduling mode is used with
mobile stations involved in a soft hand-off.
SUMMARY OF THE INVENTION
[0005] The present invention provides a method of controlling
reverse link transmissions that permits concurrently operating in
both the scheduled transmission mode and the rate control
scheduling mode. According to the present invention, the two modes
have a cooperative functional relationship that reduces the
transmission power and/or bandwidth needed on the forward link to
schedule mobile transmissions. In many cases, a reduced amount of
information may be sent on the forward link in order to schedule a
mobile's transmissions.
[0006] According to one embodiment, the scheduled transmission mode
is used to schedule a transmission and set a rate limit from which
the rate control scheduling mode operates. Namely, a mobile station
interprets a rate control bit with respect to the rate limit set by
the last schedule grant message received. In an alternative
embodiment the mobile station transmits, in response to a rate
control instruction, based on a rate of a previous transmission
made by the mobile station in response to a previous schedule grant
message.
[0007] According to another embodiment, the schedule grant message
overrides a common rate control instruction. In this embodiment,
the available load at the base station is used to determine whether
to send one or more mobile stations respective schedule grant
messages, which override the common rate control instruction for
these mobile stations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention will become more fully understood from
the detailed description given herein below and the accompanying
drawings which are given by way of illustration only, wherein like
reference numerals designate corresponding parts in the various
drawings, and wherein:
[0009] FIG. 1 illustrates communication between the mobile station
and the base station in which a first embodiment of the present
invention is employed to schedule transmission;
[0010] FIG. 2 illustrates the operational process performed at the
mobile station according to a first embodiment of the present
invention;
[0011] FIG. 3 illustrates the operational process performed at the
base station according to a first embodiment of the present
invention;
[0012] FIG. 4 illustrates the operational process performed at the
mobile station according to a second embodiment of the present
invention; and
[0013] FIGS. 5A-5B illustrate the operational process performed at
the base station according to a second embodiment of the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0014] The following description may be described as based on a
wireless communication system operating in accordance with the
cdma2000 1xEV-DV standard. Although the exemplary embodiments of
the present invention will be described in this exemplary context,
it should be noted that the exemplary embodiments shown and
described herein are meant to be illustrative only and are not
limiting in any way. As such, various modifications will be
apparent to those skilled in the art for application to other
communications systems, such as the Universal Mobile
Telecommunications System (UMTS) as reflected in the high-speed
uplink packet access (HSUPA) system specification, for example, and
are contemplated by the teachings herein.
[0015] Where used below, a mobile station (or mobile) is a device
providing data connectivity to a user. A mobile station may be
connected to a computing device such as a laptop, personal computer
(PC), or it may be a self-contained data device such as a personal
digital assistant (PDA) or cellular phone. Accordingly, a mobile
station is equivalent to, and may also be referred to as, an access
terminal, wireless mobile, remote station, user, user equipment
(UE), subscriber or any other remote user of wireless resources in
a wireless communications network. Further, a mobile station may be
functionally divided into a computing device such as a PC, which is
responsible for point-to-point protocol (PPP) and higher later
protocol functionality (IP, TCP, RTP, HTTP, etc.) and an access
terminal (AT). The AT is responsible for the airlink and radio link
protocol (RLP) layers.
[0016] Additionally as used herein, a base station refers to
network equipment providing data connectivity between a packet data
network (e.g., the Internet) and one or more mobile stations. A
base station may be equivalent to, and may also be referred to as a
base transmitter station, Node-B, access network or radio access
network (RAN). An access network or RAN may be composed of one or
more base stations.
[0017] Unification of the Control Mechanism for Scheduling and
Dedicated Rate Control
[0018] A first embodiment of the present invention provides a
method of controlling reverse link (mobile station to base station)
transmissions that cooperatively unifies the scheduled transmission
mode and dedicated rate control scheduling mode transmission
mechanisms or methods. According to the present invention, the rate
limit set by a schedule grant message in the scheduled transmission
mode has a dual function/interpretation. The schedule grant serves
not only to direct a mobile station to transmit at a specified rate
(and for a certain duration) in the well-known manner, but also
sets or resets the rate limit for subsequent transmissions
scheduled for the mobile station according to the dedicated rate
control scheduling method. Thus, the schedule grant message
provides both a rate assignment for the particular transmission as
well as a rate limit for later rate control scheduling method
transmissions.
[0019] According to one embodiment of the present invention, a base
station sends schedule grant messages over a forward link uplink
scheduling channel (F-USCH), also known as the forward grant
channel. Instructions, such as the rate control bit, sent according
to the rate control scheduling mode are sent by the base station
over a different channel. More particularly, these instructions are
sent on a sub-channel of the forward link control and
acknowledgement channel (F-UCACH), also referred to as the rate
control channel.
[0020] An example operation of the first embodiment of the present
invention will be described with respect to FIG. 1. Subsequently,
the operational process at the mobile station will be described
with respect to FIG. 2, and then the operational process at the
base station will be described with respect to FIG. 3.
[0021] FIG. 1 illustrates communication between the mobile station
and the base station in which the method of the present invention
is employed to schedule transmissions. FIG. 1 illustrates a first
time-line 10 of transmission performed by the mobile station, a
second time-line 12 of transmission performed by the base station,
and a third time-line 14 of transmission performed by the mobile
station.
[0022] As shown, particularly with respect to the first time-line
10, when the mobile station has data to send to the base station,
the mobile station enters the scheduled transmission mode and
transmits asynchronously over the reverse link packet data control
channel (R-PDCCH). The transmission notifies the base station that
the mobile station has data to transmit. More particularly, the
transmission notifies the base station that the data buffer in the
mobile station is not empty, referred to as a non-zero buffer
status. In this transmission, the mobile station also makes a first
pilot report. A pilot report indicates the signal strength (such as
the transmitted power) of a primary pilot signal transmitted by the
mobile station to the base station. This signal is referred to as
the R-PPICH (Reverse Link Primary Pilot Channel).
[0023] As shown by the first time-line 10, the mobile station will
continue periodically transmitting pilot reports, and only
interrupts the transmission of a pilot report to perform a packet
data transmission. As shown by the second time-line 12, the base
station decodes the R-PDCCH and updates information maintained on
the mobile station. For example, the base station will update
information on the buffer status of the mobile station. As a result
of this update, in a well-known manner, the base station schedules
transmission by the mobile station by sending a schedule grant
message on the F-USCH. As is well known, the schedule grant message
identifies the mobile station and contains information on the
format (rate, duration, and transmission power), and strength with
which an additional pilot is to be transmitted. This additional
pilot, also termed a secondary pilot (R-SPCIH) provides additional
data for estimating the channel at the time of data transmission.
According to the present invention, the rate given in the format of
the scheduled transmission will serve the dual role of the rate
limit for subsequent mobile station transmissions scheduled
according to the rate control scheduling method.
[0024] An alternative embodiment would use the rate at which the
mobile transmits in response to the schedule grant as the reference
rate limit. In some cases, it is possible for the mobile to make a
transmission at a rate that is lower than the granted data due to
the smaller number of bits and/or reduced power available for the
transmission.
[0025] In response to the schedule grant message, as shown by the
third time-line 14, the mobile station transmits reverse link
secondary pilot channel (R-SPICH) and R-PDCCH frames and a
corresponding reverse link packet data channel (R-PDCH) frame. As
is well-known, the R-PDCCH carries the control and format
information for the data being transmitted by the mobile station
over the R-PDCH. As is further well-known, the R-SPICH is a
secondary pilot channel sent by the mobile station. However,
according to the present invention, the mobile station sets the
power at which the secondary pilot channel is transmitted based on
the rate indicated in the schedule grant message. Specifically, the
mobile station includes a look-up table mapping rate to secondary
pilot channel powers.
[0026] The base station receives and decodes the mobile station
transmission and sends acknowledgement (ACK) or
negative-acknowledgement (NACK) feedback to the mobile station. An
ACK indicates that the transmission was received and decoded
successfully. A NACK indicates that the transmission was not
properly received and/or decoded. As is well-known, in response to
a NACK, the mobile station will attempt a re-transmission. In this
descriptions re-transmissions are asynchronous, i.e. the
re-transmission may follow an arbitrary time after the
transmission, and the base station will indicate to the mobile when
it should make the retransmission.
[0027] The mobile station continues to send pilot reports to the
base station as shown in the first time-line 10. The base station
may schedule another transmission by the mobile station by either
sending a schedule grant message or by utilizing the rate control
scheduling method. As will be appreciated, and as described in
greater detail below, in accordance with the principals of this
embodiment of the present invention, the mobile station will
monitor both the F-USCH and the F-UCACH.
[0028] As will further be appreciated, scheduling in the rate
control scheduling mode is much simpler and requires fewer
resources (e.g., power, bandwidth, duration of the channel is used)
to schedule a transmission. FIG. 1 illustrates that the subsequent
scheduling of the mobile station is performed according to the rate
control scheduling method. As shown in the second time-line 12, the
base station sends a single-bit rate control instruction. In one
embodiment of the present invention, the mobile station operates
according to the on-off keying technique. Accordingly, when the
rate control bit is set/transmitted (as opposed to silence), the
mobile station interprets the rate control instruction as
scheduling a transmission with a rate limit as set in the
previously received schedule grant message.
[0029] The present invention, however, is not limited to this
embodiment of rate control scheduling. Instead, the rate control
bit or bits may indicate whether the mobile station is to transmit
at an increased or decreased rate limit with respect to the rate
limit set in the previously received schedule grant message. Thus
the scheme would use the rate control bits to increase or decrease
the rate limit with respect to the rate limit set in the previously
received schedule grant if the previous transmission is made in
response to the schedule grant, or with respect to the previous
rate limit if the previous transmission is made in response to the
rate control bit. Also, the adjustments to the rate limit set by
the previously received schedule grant can be cumulative so that
all rate control bits received between the current transmission
instant and the previously received schedule grant are used to
determine the current rate limit. Alternatively, the rate control
bits may indicate an increase or decrease with respect to the rate
of the mobile station's last transmission, and the adjustments to
the rate limit, due to successive rate control bits may accumulate.
As a further example, the rate control bit or bits may be used to
probabilistically influence the rate limit set in the previously
received schedule grant message if the previous transmission is
made in response to the schedule grant, or probabilistically
influence the previous rate limit if the previous transmission is
made in response to the rate control bit(s). The rate control
bit(s) may also indicate a change (or no change) with respect to
the rate with which the mobile station made its transmission in
response to the schedule grant.
[0030] If the mobile station still has data in its buffer, then in
response to the rate control instruction, the mobile station
transmits R-SPICH and R-PDCCH frames and a corresponding reverse
link packet data channel (R-PDCH) frame in the same manner
described previously. If this transmission will empty the buffer of
the mobile station, the mobile station indicates a zero buffer
status in the R-PCCH frame.
[0031] Assuming the transmission by the mobile station is received
and decoded, the base station, besides acknowledging the
transmission, sends a release message for the mobile station over
the F-USCH in response to the indicated zero buffer status. In
response to the release message, the mobile station will halt the
periodic sending of the pilot updates.
[0032] As discussed above, the base station may schedule subsequent
transmissions according to either the rate control scheduling
method or the scheduled transmission method. If the scheduled
transmission method is reused, then the schedule grant message sent
will serve to reset the rate limit upon which the rate control
scheduling method is based. Furthermore, while an asynchronous
operation of rate control scheduling was described above and will
be described in further detail below, performing scheduling
according to the principals of the present invention for
synchronous rate control scheduling will be readily apparent from
the proceeding and following disclosure.
[0033] Next, the operational process at the mobile station will be
described with respect to FIG. 2. As shown, after the mobile
station sends the initial buffer status and the pilot report to
enter the scheduling mode, the mobile station monitors the F-USCH
and attempts to decode the F-USCH every scheduling interval in step
S20. Then, in step S22, the mobile station determines if the
decoded schedule grant message is for itself. If so, then in step
S24 the mobile station performs a transmission according to the
transmission format (rate, duration, etc.) set in the schedule
grant message, and will set the rate limit as that indicated by the
schedule grant message.
[0034] If in step S22 the mobile station does not determine that a
schedule grant message is intended for itself, then in step S26,
the mobile station monitors the F-UCACH for a rate control
instruction. If a rate control instruction is sent during the
scheduling interval, then the mobile station uses the rate limit
from the previous schedule grant message as the rate limit for
performing a transmission according to the rate control scheduling
method. Alternatively, the rate control scheduling method employed
may, for example, be any of the above-discussed embodiments. For
instance, the rate control could be performed with respect to the
previous rate limit if the previous transmission is made in
response to the rate control bit, and/or the adjustments to the
rate limit set by the previously received schedule grant can be
cumulative so that all rate control bits received between the
current transmission instant and the previously received schedule
grant are used to determine the current rate limit. If no rate
control instruction is received in step S26, then processing
returns to step S20. Processing also returns to step S20 after
steps S24 and S28.
[0035] While the operational process has been described for
asynchronous rate control scheduling, it will be appreciated from
the previous and following disclosure that synchronous rate control
scheduling could be performed. For example, the second embodiment
of the present invention described in detail below will discuss a
synchronous rate control operation that is readily applicable to
this embodiment of the present invention. For instance, step S46,
S48 and S50 of FIG. 4 may be added between steps S22 and S26 of the
present invention to obtain a synchronous rate control
operation.
[0036] Next, the operational process at the base station will be
described with respect to FIG. 3. As shown, the base station uses
any well-known method to prioritize the scheduling of transmissions
by mobile stations, and determines in step S30 if the priority
established for the mobile station permits scheduling of
transmission by the mobile station. Once the priority of the mobile
station permits scheduling transmission, the base station
determines in any well known manner the optimum transmission format
(rate, duration and power) for the mobile station transmission in
step S32.
[0037] Then, in step S34, the base station determines if an
absolute value of the currently determined rate minus the previous
rate (i.e., rate limit) assigned to the mobile station is greater
than a predetermined threshold. Namely, the base station determines
if the change in assigned rate limit exceeds a threshold amount. If
so, then the base station schedules transmission of the mobile
station according to the scheduled transmission mode by sending a
scheduling grant message over the F-USCH in step S36. If the change
in assigned rate limit does not exceed the threshold amount, then
the base station schedules transmission of the mobile station
according to the rate control scheduling method by sending a rate
control instruction in step S38.
[0038] The previously described base station procedure shows how a
decision is made to send a rate control command versus a schedule
grant to a user that has been deemed high priority and required to
transmit data. The description was in the context of a system that
combined scheduling with dedicated on-off rate control with
asynchronous operation. The base station procedures may also
include procedures for determining the control messages to be sent
to all the users taking into account the maximum load at the base
station as well as the currently assigned rate limits. The maximum
load is a measure of the received power that the base station can
tolerate for normal operation of the reverse link for all mobiles
in the cell. The maximum load and current rate limits are metrics
that would determine the pools of users to be scheduled versus rate
controlled, the actual rate limits for all users, and the control
message (schedule grant or rate control command) to be sent to the
users. The next embodiment of the present invention will describe
base station procedures for determining the control messages to be
sent to all the users taking into account the maximum load at the
base station as well as the currently assigned rate limits. This
procedure is described with respect to FIGS. 5A and 5B and is
readily applicable to the above described embodiment of the present
invention. For example, the above-described embodiment of the
present invention may adopt the procedures of FIGS. 5A and 5B,
except that steps S68-S72 would be replaced with the steps of (i)
prioritizing the rate control mobiles based on channel conditions,
transmit power headroom, data in their respective buffers, etc. in
the any well-known manner; and (ii) determine individual rat
control bit(s) based on the mobile priority and the available load
at the base station. Namely, in step (ii) the highest priority
mobiles are considered first, and if the available load permits
rate control scheduling of the mobile, then the mobile is rate
controlled schedule; otherwise, the mobile is not scheduled.
[0039] Unification of the Control Mechanism for Scheduling and
Common Rate Control
[0040] A common rate control or scheduling mechanism is one where
the data transmissions of a number of mobile stations are scheduled
or controlled by a single or common set of rate control bits. One
example of common rate control is the HRPD (high rate packet data)
system based on the IS-856 standard. In this system, the rate
control bits known as reverse activity bits (RAB) are broadcast to
all mobile stations in a sector. The received RAB bits (indicating
to adjust power up or down) are used by the mobile stations to ramp
up or ramp down their data transmission rates with pre-determined
transition probabilities. The data rates used by the mobile
stations typically move up and down in tandem within a small band
of data rates. Common rate control is also under consideration for
the enhanced reverse link of 1xEV-DV Revision D (IS-2000-D).
[0041] A weakness of a common rate control scheme is its inability
to give priority to individual mobile station's data transmissions.
Low-latency, high data transmissions by a single (or small number
of) mobile station(s) is often desirable in order to meet quality
of service (QoS) requirements.
[0042] According to a second embodiment of the present invention,
the control mechanisms for scheduled transmission and common rate
control scheduling are integrated by using a schedule grant message
to override the rate limit implied by the sequence of common rate
control bits received by the mobiles.
[0043] For the purposes of example only, the second embodiment of
the present invention will be described using the common rate
control scheduling scheme of HRPD as an exemplary common rate
control scheduling scheme, but it will be recognized that the
present invention is not limited to this common rate control
scheduling scheme.
[0044] The second embodiment of the present invention will also be
described in the context of a system with synchronous
acknowledgements and retransmissions. An acknowledgement is said to
be synchronous if there exists a fixed timing relationship between
transmission of a data packet and the acknowledgement of its
successful or unsuccessful receipt at the receiver. Similarly
synchronous retransmissions occur a fixed time interval after
unsuccessful reception of a data transmission.
[0045] The use of the control mechanism described here may be
extended in a straightforward manner to the cases where either the
acknowledgements, retransmissions, or both are asynchronous, i.e.
do not maintain a fixed timing relationship with the initial data
transmission.
[0046] Examples of the mobile station and base station procedures
to be used when a schedule granting mechanism is integrated in a
system with common rate control scheduling will be described with
respect to FIGS. 4 and 5A-5B, respectively.
[0047] FIG. 4 illustrates the operational process performed at the
mobile station according to a second embodiment of the present
invention. As shown, the mobile station monitors the F-USCH and
attempts to decode the F-USCH every scheduling interval in step
S40. Then, in step S42, the mobile station determines if the
decoded schedule grant message is for itself. If so, then in step
S44 the mobile station performs a transmission according to the
transmission format (rate, duration, etc.) set in the schedule
grant message. However, the mobile station continues to maintain a
rate limit that is the previously transmitted rate control rate
(PTRR) in step S45. The PTRR is defined as the actual data rate of
the mobile station's previous transmission on the R-PDCH while
acting upon the rate control instruction (e.g., RAB). When the
mobile transmits on the R-PDCH while acting upon the explicit
scheduling grant message or, as described later, upon the
re-transmission command (i.e., NACK signal sent by the base
station), the PTRR is not changed.
[0048] If in step S42 the mobile station does not determine that a
schedule grant message is intended for itself, then in step S46,
the mobile station determines whether an acknowledgement for a
prior transmission is expected. If so, then in step S48, the mobile
station determines if an ACK or NAK is received. If a NACK is
received, then as described above, the mobile station retransmits
based on the schedule grant for the NACKed transmission in step
S50. Particularly, the rate from the scheduled grant message is
used for the retransmission. However, the mobile station does
maintain the rate limit that is the PTRR in step S45.
[0049] If an ACK is received in step S48 or no acknowledgement is
expected in step S46, then in step S52 the mobile station monitors
the RAB. If RAB are sent during the scheduling interval, then the
mobile station determines the transmission rate limit from the RAB
and the PTRR in any well known manner, and transmits data on the
R-PDCH using a rate that is equal to or less than the rate limit if
the mobile station's buffer is not empty. The PTRR is then updated
to the actual transmission rate. If, in step S52, the mobile
station does not detect RAB on the F-UCACH, then processing
proceeds to step S45. After steps S45 and S54, processing proceeds
to step S40.
[0050] As described above, if a schedule grant message is received,
the rate in the schedule grant message overrides the rate limit
from the received RAB bits meanwhile the PTRR is not updated. And,
for subsequent frames, if no further scheduling grant messages are
received, the rate limit is determined from the received RAB bits
and the PTRR then the PTRR is updated, except if a retransmission
of a previously scheduled transmission is required.
[0051] Next, the operational process at the base station will be
described with respect to FIGS. 5A-5B. As shown, the base station,
in any well known manner (e.g., based on the previous decoding
results), determines the set of mobile stations that require a new
transmission excluding mobile stations with pending retransmission
during the frame in step S60. Then in step S62, the base station
determines the supportable rate for each mobile station in the set
based on the channel conditions, transmit power headroom, data in
the buffer of each mobile station, etc. Because step S62, like step
S60, is so well known, this step will not be described in
detail.
[0052] Subsequently, in step S64, the base station prioritizes the
mobile stations for scheduling. In one embodiment of the present
invention, the prioritizing is performed based on the rate
difference between the supportable rate determined in step S62 and
the current rate limit set forth by the RAB. Specifically, the base
station ranks the mobile stations having the greatest rate
difference from highest priority to lowest priority, and places the
ranked mobile stations having a rate difference greater than a
predetermined threshold on a scheduling list.
[0053] Next, in step S66, the base station determines which mobile
stations on the scheduling list to schedule according to the
scheduled transmission method and which mobile stations to schedule
according to the common rate control scheduling method.
Furthermore, in step S66, the base station determines the rate
among other things (e.g., transmission format) for the mobile
stations being scheduled according to the scheduled transmission
method. FIG. 5B illustrates a flow chart showing the process steps
performed by the base station in performing step S66.
[0054] As shown in FIG. 5B, the base station starts with the
highest priority mobile station on the scheduling list as the
mobile station under consideration; hereinafter, the considered
mobile station. Then, in step S80, the base station determines if
the available load is less than zero. In general, load is the
accumulated signal power of each mobile station's transmission.
However, a base station has a maximum load that it can support. The
available load is the maximum supportable load minus a currently
expected load from mobile station transmissions. At the beginning
of the scheduling procedure, the available load is determined as
the maximum load minus the combination of
[0055] the load that retransmissions of data packets would cause;
and
[0056] the sum of PTFRR_DOWN_rate loads of the mobile stations in
the set (see step S60) of mobile stations.
[0057] PTRR_DOWN_rate load is defined as the load contribution of a
new transmission if the transmission were made in response to RAB
of DOWN sent by the base station and the mobile station made the
new transmission by acting upon this DOWN command probabilistically
with respect to its PTRR. More specifically, as is well known with
respect to common rate control according to HRPD,
PTRR_DOWN_rate load=(the probability that mobile transmits at (PTRR
down by one step rate) times the load of (PTRR down by one step
rate))+(the probability that mobile transmits at PTRR rate times
the load of PTRR rate)
[0058] Similarly,
PTRR_UP_rate load=(the probability that mobile transmits at (PTRR
up by one step rate) times the load of (PTRR up by one step
rate))+(the probability that mobile transmits at PTRR rate times
the load of PTRR rate)
[0059] It will further be appreciated, as is well known with
respect to common rate control according to HRPD, the rate
transition probabilities for each PTRR can be different and are
known at both the base station and the mobile station
[0060] If in step S80, the base station determines that the
available load is not less than zero, then in step S82, the base
station determines if the available load plus the PTRR_DOWN_rate
load of the considered mobile station is greater than the load if
the considered mobile station made a transmission at its
supportable rate (which was determined in step S62).
[0061] If the determination in step S82 is positive, then in step
S84, the base station schedules the considered mobile station for
transmission according to the scheduled transmission method and at
the considered mobile station's supportable rate. Next, in step
S86, the base station updates the available load by (i) adding the
PTRR_DOWN_rate load of the considered mobile station and (ii)
subtracting the load if the considered mobile station made a
transmission at its supportable rate.
[0062] Then in step S88, the base station determines if the any
other mobile stations remain on the scheduling list. If so, then in
step S90, the next mobile station in terms of priority on the
scheduling list becomes the considered mobile station, and
processing returns to step S80.
[0063] Returning to step S82, if the determination in this step is
negative, then processing proceeds directly to step S88. An
alternative at this step is to determine a lower supportable rate
for the mobile that would satisfy the test of step S82. If such a
rate exists and is substantially different from the mobile's
current rate limit, then step S84 is entered. If not, step S88 is
entered. In step S88, if the scheduling list has been exhausted,
then processing proceeds to step S92. Also, if in step S80, the
base station determines that the available load is less then zero,
then processing proceeds to step S92.
[0064] In step S92, the base station treats the unscheduled mobile
stations on the scheduling list as rate controlled mobiles. Namely,
these mobile stations will be scheduled according to the common
rate control scheduling method, as will the mobile stations that
did not make the scheduled list but formed part of the set of
mobile stations determined in step S60.
[0065] Returning to FIG. 5A, after step S66, the base station
determines in step S68 if (i) the available load resulting from
step S66 plus (ii) the sum of the PTRR_DOWN_rate loads of the rate
controlled mobile stations is greater than the sum of the
PTRR_UP_rate loads of the rate controlled mobile stations. If so,
then in step S70, the base station schedules the rate controlled
mobiles according to the common rate control scheduling method by
sending RAB set to UP. If the determination in step S68 is
negative, then in step S72, the base station schedules the rate
controlled mobile stations according to the common rate control
scheduling method by sending RAB set to DOWN. In an alternative
approach to steps S68-S72 where the RAB is a three-state (Up, Hold,
and Down) indication, two thresholds are tested. Here, if the
available load plus the sum of loads of all rate-controlled
mobiles' PTRR_Down_rates is greater than the sum of loads of all
rate-controlled mobiles' PFRR_Up_rates, RAB is set to Up; else if
the available load plus the sum of loads of all rate-controlled
mobiles'PTRR_Down_rates is greater than the sum of loads of all
rate-controlled mobiles' PTRRs, the RAB is set to Hold; else the
RAB is set to Down. Other rate control alternatives, such as those
described previously in this disclosure, may also be used in place
of steps S68-S72.
[0066] As will be appreciated, in the second embodiment, the
available load determines the assigned rates. Namely, scheduling of
individual mobile stations is possible in conjunction with common
rate control scheduling. After an individual rate is assigned to
each scheduled mobile station, the available load is recalculated
by subtracting the additional load that is due to the newly
scheduled transmission. Rate-controlled mobile stations are then
defined as those mobile stations that are not scheduled or are not
re-transmitting.
[0067] In the second embodiment, an alternative method for the
mobile to determine the power level on the R-SPICH can be based on
the power levels for the rates that the mobile can possibly choose
to transmit and the probabilities that the mobiles choose those
rates. More specifically, mobile_R-SPICH_power=sum of (R-SPICH
power if rate i is transmitted times the probability that the
mobile chooses rate i to transmit) over i, for i is any rate that
the mobile can choose to transmit in response to the RAB and the
PTRR. Since the transition probabilities are known to both the base
station and mobile station, there is no ambiguity regarding what
power level to be used on the R-SPICH. After the mobile selects a
particular rate j, the mobile will apply an adjustment to the
traffic-to-pilot ratio on the packet data channel to ensure the
power level of the packet data channel is correct for the fmal
selected rate j (i.e. to correct any deficits if the R-SPICH power
of rate j is higher than the MS_R-SPICH_power or any surpluses if
the R-SPICH power of rate j is lower than the
MS_R-SPICH_power).
[0068] The invention being thus described, it will be obvious that
the same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications are intended to be included within the
scope of the following claims.
* * * * *